Electrical/visual differential pressure indicator with solid state sensor

ABSTRACT

A method of determining fouling of a filter includes the use of a differential pressure indicator which has a housing with at least two ports in the housing. One port receives a first pressure, and the second port receives a second pressure. A pressure resistive device is placed between the first port and the second port, and changes its position when the first pressure exceeds the second pressure by a predetermined amount. A magnet is coupled to the pressure resistive device. A digital displacement sensor senses the position of the magnet and is in communication with an electronic indicator. The electronic indicator activates when the first pressure exceeds the second pressure by a predetermined amount, thus allowing determination of filter fouling.

RELATED APPLICATION DATA

[0001] This is a divisional of application Ser. No. 10/334,085, filedDec. 30, 2002, now U.S. Pat. No. ______.

FIELD OF INVENTION

[0002] The present invention is directed generally to a differentialpressure indicator, and more specifically, to a differential pressureindicator incorporating the use of a digital displacement sensor, and toa method of using same to determine filter fouling.

BACKGROUND

[0003] Many attempts have been made in the past to provide a mechanismfor monitoring the condition of a filter in either a fluid or gaseousenvironment and to detect whether a filter element must be replaced orreconditioned before continuing operation. These devices are, forexample, used in hydraulic systems to provide a visual or electricalsignal (or a combination of both) when differential pressures across afilter element exceed a set value. Devices of this nature have beenfashioned in electrical forms, mechanical forms, or a combination ofboth. However, problems have arisen with the said devices.

[0004] The most cost-efficient indicators to date utilize a combinationof mechanical and electrical elements. In these hybrid indicators, amechanical micro switch is used to provide a signal by opening orclosing an electrical circuit. However, the use and reliability of amicro switch is limited when low currents (less than 0.5 amp) arerequired. Additionally, many applications require hermetically sealedswitches, which in turn increase the size, weight, and cost of theindicator.

[0005] Thus, there is a need for reliable, small, inexpensivedifferential pressure indicators that can work with low currents and abroad range of temperatures, especially for applications involvinghydraulic systems in aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 depicts a cut-away view of a differential pressureindicator in a non-actuated state according to an embodiment of thepresent invention;

[0007]FIG. 2 depicts an electrical schematic of a control moduleincorporating a circuit board according to an embodiment of the presentinvention;

[0008]FIG. 3 depicts a cut-away view of a differential pressureindicator in an actuated state according to an embodiment of the presentinvention;

[0009]FIG. 4 depicts a cut-away view of a differential pressureindicator in a non-actuated position according to an alternativeembodiment of the present invention;

[0010]FIG. 5 depicts an electrical schematic of a control moduleincorporating a microcontroller according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

[0011] Embodiments of the present invention are directed to differentialpressure indicators incorporating pressure-resistive devices and digitaldisplacement sensors to measure filter performance characteristics.Various pressure-resistive devices may be used depending on the relevantpressures involved in the application. Similarly, various electricalindicators may be used depending on the relevant application of thedifferential pressure indicator. Embodiments of the present inventionmay be used in either gas pressure or fluid pressure applications.

[0012] The differential pressure indicator presented herein replaces themechanical micro switch of previous designs with a solid state digitaldisplacement sensor. The use of a non-mechanical electrical switch andelectronic indicator significantly reduces the part count compared withexisting differential pressure indicator designs. The reduction in partcount also has an immediate impact on assembly component cost and hasthe added benefit of improving reliability in both low and highdifferential pressure applications regardless of the system pressure.Differential pressure indicators are less susceptible to shock andvibration, smaller in size and more suitable to low currentapplications. Furthermore, digital displacement sensors provide asignificant cost savings over micro switches.

[0013] The reduction of moving parts along with the robustness of solidstate electronics enhances the reliability and capability of theindicator. Additionally, with this approach, the operating and releasepoints can be maintained within a few pounds per square inchdifferential (“PSID”), even over a wide range of voltage inputs.According to the preferred embodiment of the invention, the differentialpressure indicator can work with voltages ranging from 3.8 to 30 VDC andcan operate with a current supply as low as 10 mA. Additionally, thisindicator can work within operating temperatures ranging from −40° F. to+302° F.

[0014]FIG. 1 depicts a cut-away view of a differential pressureindicator in a non-actuated state according to a preferred embodiment ofthe present invention. The differential pressure indicator, according tothis embodiment, includes a housing 10, a high pressure port 20, a lowpressure port 30, a spring 40, a chamber 110 housing a piston 50, amagnet 60, a digital displacement sensor 70, a control module 80, alight-emitting diode (“LED”) 90, and leads 100. According to theembodiment of FIG. 1, a pressure upstream from a filter element isported to the high pressure port 20 that is ported through the housing10, and the upstream pressure pushes on one end of the piston 50, whichresides in a chamber 110 in the housing 10. A pressure downstream from afilter is ported to the low pressure port 30, also ported through thehousing 10, and the downstream pressure pushes on the opposite end ofthe piston 50. The piston 50 is coupled to the spring 40 at one end, andthe permanent magnet 60 at the other. The magnet 60 provides a magneticfield that affects the digital displacement sensor 70. The digitaldisplacement sensor 70 is coupled to the control module 80, and themagnetic field of the magnet 60 causes the digital displacement sensor70 to output a different digital signal to the control module 80 than itwould otherwise if the magnetic field were not present. The controlmodule 80 is electronically coupled to the LED 90, and the leads 100.The leads 100 allow for remote sensing, such as coupling the leads to anLED located some distance from the differential pressure indicator, forinstance, in an instrument panel in the cockpit of an airplane.

[0015] When the differential pressure indicator is in a non-actuatedstate as shown in FIG. 1, the magnet 60 is in the presence of thedigital displacement sensor 70, and the magnetic field produced by themagnet 60 causes the digital displacement sensor 70 to produce a certaindigital signal to the control module 80.

[0016]FIG. 2 depicts a control module according to an embodiment of thepresent invention wherein the control module is an electronic circuit.In FIG. 2, a voltage regulator 200 is in electrical communication withthe digital displacement sensor 70. The voltage regulator 200 receivespower from an external supply, for instance, from an airplane's batteryor alternator. The incorporation of the voltage regulator increases thelife of the electrical components and allows the differential pressureindicator to work across a broad range of voltage inputs. The voltageregulator changes the voltage input it receives to a voltage output thatcan be specifically used by the circuit. For example, the voltageregulator 200 accepts 30 VDC from the power source and drops the voltageto 5 VDC. The regulator 200 operates to maintain the output supplyvoltage at 5V, for example, even if the load which it is suppliedchanges.

[0017] In FIG. 2, when the differential pressure indicator is in anon-actuated state, the digital displacement sensor 70 is in themagnetic field of the magnet 60 and is producing a digital signal of “1”(voltage=5VDC), so that no voltage potential exists across the LED 90.When the digital displacement sensor is not within the magnetic field ofthe magnet 60, the digital displacement sensor 70 produces a digitalsignal of “0” (voltage≠1V), this allows the voltage from the regulatorto be applied across the LED 90, energizing the LED 90. In a preferredembodiment, if the primary power source is removed, as when the aircraftis turned off when parked, for example, the electronic indicator remainsactivated by an embedded power source. The embedded power source is asecondary power source to a primary power source that powers thecircuit. In FIG. 2, the embedded power source is depicted as a capacitor210, according to one embodiment of the present invention. According toanother embodiment, the embedded power source may be a battery.

[0018] In an embodiment of the invention using an electronic circuit asa control module, C1 is a 1 μF 100V capacitor, C2 is a 1500 nF 50Vcapacitor, C3 and C5 are 2.2 μF 10V capacitors, C4 is a 1.0 Farad GoldCAP capacitor, D1-D3 are Schottky 30 V 30 mA diodes, D4 is a 3MM LED, R1is a 43.2KΩ resistor, R2 is a 12.1KΩ resistor, R3 is a 2KΩ resistor, andthe DDS is the digital displacement sensor PTI P/N 7594207-101. Thepresent invention is not limited to the illustrated embodiment, and oneskilled in the art may easily modify this circuit and/or its values toaccomplish the same goals with different configurations. Furthermore,while this schematic depicts an embodiment where the digitaldisplacement sensor 70 produces a digital value of “1” in the presenceof a magnetic field and “0” otherwise, one skilled in the art couldeasily manipulate this schematic such that the digital displacementsensor 70 produces a digital value of “0” in the presence of a magneticfield and “1” otherwise.

[0019]FIG. 5 depicts a control module according to a preferredembodiment of the present invention wherein the control module is amicrocontroller. In FIG. 5, a voltage regulator 200 is in electricalcommunication with a microcontroller 500, a digital displacement sensor70, and the secondary power source, in this case, a capacitor 510. InFIG. 5, when the differential pressure indicator is in a non-actuatedstate, the digital displacement sensor 70 is in the magnetic field ofthe magnet 60 and is outputting a digital signal of “1” (voltage=5VDC),to the microcontroller 500. When the digital displacement sensor is notwithin the magnetic field of the magnet 60, the digital displacementsensor 70 outputs a digital signal of “0” (voltage≠1V) to themicrocontroller 500. The microcontroller 500 determines the amount oftime that the digital displacement sensor 70 has been outputting adigital signal of “0.” If the digital displacement sensor 70 outputs adigital signal of “0” for less than two (2) seconds, then LED1 520 isactivated. If the digital displacement sensor 70 outputs a digitalsignal of “0” for more than two (2) seconds, but less than five (5)seconds, then LED2 530 is activated. If the digital displacement sensor70 outputs a digital signal of “0” for more than five (5) seconds, butless than ten (10) seconds, LED3 540 is activated. And if the digitaldisplacement sensor 70 outputs a digital signal of “0” for more than ten(10) seconds, LED4 550 is activated.

[0020] The addition of multiple LED's that sequentially activate basedupon a signal's temporal measurement alert to the possibility of “falsepositives” caused by pressure spikes. That is, occasionally a systemexperiences a pressure spike that is not caused by the fouling of afilter, but rather by some other anomaly. These pressure spikescharacteristically only occur for a short period of time, for example aperiod of three or four seconds. The use of a microcontroller alerts tothe presence of a pressure spike as opposed to the fouling of a filterand saves needless examination or replacement of the filter. However, ifthe differential pressure surpasses the actuation differential pressurefor longer than ten (10) seconds (thus causing the digital displacementsensor 70 to output a digital signal of “0” for longer than ten (10)seconds), the cause is most likely due to a fouled filter and not apressure spike. Thus, if LED4 520 activates, it alerts that the filteris most likely fouled and needs examination or replacement.

[0021] In a preferred embodiment of the differential pressure indicatorincorporating the use of a microcontroller, if the primary power sourceis removed, as when the aircraft is turned off when parked, for example,the electronic indicator remains activated by an embedded power source.In FIG. 5, the embedded power source is depicted as a capacitor 510,according to one embodiment of the present invention. According toanother embodiment, the embedded power source may be a battery.

[0022] In an embodiment of the present invention incorporating the useof a microcontroller as a control module, the microcontroller isMicrochip PIC12C Family Part Number PIC12C509A, the digital displacementsensor is Honeywell Digital Position Sensor Model No. SS449A, C1 is aResin Dipped Solid Tantalum, 35 VDC 0.1 mF capacitor, C2 is a CeramicDisc, 25 V 0.1 mF capacitor, R1 is a Metal Film, 0.25W 100KΩ resistor,R2 is a Metal Film, 0.25W 33KΩ resistor, R3-R6 are Metal Film, 0.25W 1KΩresistors, and LED1-LED4 are Amber 1.5 VDC 20 mA Light Emitting Diodes.The present invention is not limited to the illustrated embodiment, andone skilled in the art may easily modify this circuit and/or its valuesto accomplish the same goals with different configurations. Furthermore,while this schematic depicts an embodiment where the digitaldisplacement sensor 70 produces a digital value of “1” in the presenceof a magnetic field and “0” otherwise, one skilled in the art couldeasily manipulate this schematic such that the digital displacementsensor 70 produces a digital value of “0” in the presence of a magneticfield and “1” otherwise.

[0023]FIG. 3 depicts a differential pressure indicator in an actuatedstate according to a preferred embodiment of the present invention. Inthe actuated state, the pressure flowing upstream of a filter, portedthrough the high pressure port 20, is higher than the pressure flowingdownstream and ported through the low pressure port 30. This differencein pressure tends to push the piston 50 towards the low pressure port30. If the upstream pressure being ported through the high pressure port20 exceeds the downstream pressure being ported through the low pressureport 30 by a specified value (the actuation differential pressure), thenthe piston/magnet combination will move far enough away from the digitaldisplacement sensor 70 such that the magnetic field no longer engagesthe digital displacement sensor 70. When the digital displacement sensor70 is no longer engaged by the magnetic field, it causes the powerflowing through the circuit 80 to pass through the LED 90, activatingit.

[0024] The specific actuation differential pressure, that is, thedifference in pressure between the upstream pressure and the downstreampressure that causes the LED 90, or other suitable electronic indicator,to activate may be set by varying the strength and tension of the spring40.

[0025]FIG. 4 shows a cut-away view of a differential pressure indicatorwith a diaphragm assembly as its pressure resistive device. Forapplications involving low differential pressures, i.e., differentialpressures below 15 PSID, a preferred embodiment utilizes a diaphragmassembly. FIG. 4 is similar to FIG. 1 except that the piston assemblyhas been replaced with a diaphragm assembly. In this embodiment of theinvention, upstream pressure is ported through the high pressure port 20such that the upstream pressure presses against one side of thediaphragm 400. Downstream pressure is ported through the low pressureport 30 and pushes against the opposite side of the diaphragm 400. Aconnecting rod 410 passes through the diaphragm 400 and is coupled tothe spring 40 at one end and a magnet 60 at the other. When the upstreampressure exceeds the downstream pressure, the differential pressurepushes the diaphragm 400 towards the low pressure port 30. The movementof the diaphragm 400 causes the connecting rod 410 to move towards thelow pressure port 30 as well, withdrawing the magnet 60 from thepresence of the digital displacement sensor 70. When the differentialpressure exceeds the actuation differential pressure, the magnet 60 willhave moved far enough away from the presence of the digital displacementsensor 70 so that the magnetic field of the magnet 60 no longer engagesthe digital displacement sensor 70. When the digital displacement sensor70 is no longer engaged by the magnetic field, the digital placementsenor 70 causes power to pass through the LED 90, activating it.

[0026] Another embodiment of the present invention utilizes any suitablepressure resistive device or module in the place of the piston assemblyor diaphragm assembly.

[0027] In another embodiment of the present invention, any suitable typeof electronic indicator may be utilized, replacing the light-emittingdiode present in FIGS. 1, 2, and 3. The purpose of the electronicindicator is to provide a visual or auditory alert indicating that afilter may require cleaning, replacement, or examination.

[0028] In another embodiment of the present invention, no light emittingdiode or other electronic indicator is present in the differentialpressure indicator itself. Instead, a set of leads are used toelectronically couple the differential pressure indicator to anelectronic indicator located some distance away from the differentialpressure indicator, for example, to a light-emitting diode located inthe cockpit of the airplane. Another embodiment of the present inventionmay only have the electronic indicator, for instance an LED,electronically coupled to the circuit, leaving the leads off completely.In still another embodiment of the present invention, both the on-boardlight emitting diode, or other electronic indicator, and leads arepresent. This design has the added benefit of having an alert locatedsome distance away from the actual differential pressure indicator, forexample, in the cockpit of an airplane, and an alert at the actual siteof the indicator so that when maintenance is required, the specificdifferential pressure indicator may be easily identified.

[0029] In one embodiment of the present invention, the housing 10 ismade of metal. In another embodiment of the invention, the housing 10 ismade of plastic or other suitable material.

[0030] In one embodiment of the present invention, the digitaldisplacement sensor outputs a digital signal of 1 when the magneticfield of the magnet is present, and a digital signal of 0 when it isnot. In another embodiment, the signals are reversed and when themagnetic field is present, the digital displacement sensor outputs adigital signal of 0 and when it the magnetic field is removed, itoutputs a digital signal of 1.

[0031] While the description above refers to a particular embodiment ofthe present invention, it will be understood that many modifications maybe made without departing from the spirit thereof. The accompanyingclaims are intended to cover such modifications as would fall within thetrue scope and spirit of the present invention. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, rather than the forgoing description,and all changes that come within the meaning and range of equivalency ofthe claims are therefore intended to be embraced therein.

What is claimed is:
 1. A method of determining a fouling status of a filter, comprising: measuring a differential pressure between a flow upstream from the filter and a flow downstream from the filter; causing, by means of a solid state digital displacement sensor, an electronic indicator to activate when the differential pressure is higher than a set value; and determining the fouling status of the filter based on the activation of said electronic indicator.
 2. The method of claim 1, wherein the electronic indicator is a light emitting diode (LED).
 3. The method of claim 1, wherein the electronic indicator is an auditory alert.
 4. The method of claim 1, wherein said differential pressure is measured by a measurement device comprising: a housing having a first port to which the upstream flow pressure is ported and a second port to which the downstream flow pressure is ported; a pressure resistive device located between the first port and the second port, wherein the pressure resistive device changes its position when the upstream pressure exceeds the downstream pressure by a predetermined amount; and a magnet coupled to the pressure resistive device.
 5. The method of claim 4, wherein the electronic indicator is activated based on a position of the magnet as detected by the solid state digital displacement sensor.
 6. The method of claim 4, wherein the electronic indicator is located remotely from the housing of the measurement device.
 7. The method of claim 4, wherein the measurement device further comprises a control module, said module being electrically coupled to the solid state digital displacement sensor and in communication with the electronic indicator, said electronic indicator being activated based on a position of the magnet as detected by the solid state digital displacement sensor.
 8. The method of claim 7, wherein the control module is an electronic circuit.
 9. The method of claim 7, wherein the control module is a microcontroller.
 10. The method of claim 9, wherein the measurement device includes a plurality of electronic indicators sequentially activating according to a schema based on temporal measurements of signals from the solid state digital displacement sensor.
 11. The method of claim 4, wherein the pressure resistive device includes a piston assembly having a piston and a spring coupled to a first end of the piston, said magnet being coupled to a second end of the piston.
 12. The method of claim 4, wherein the pressure resistive device includes a diaphragm assembly having a diaphragm and a connecting rod, wherein a spring is coupled to a first end of the connecting rod and the magnet is coupled to a second end of the connecting rod, and the connecting rod is coupled to the diaphragm at a location between the first end and the second end of the connecting rod.
 13. A method of determining a fouling status of a filter, comprising: (a) measuring a differential pressure between a flow upstream from the filter and a flow downstream from the filter; (b) causing, by means of a solid state digital displacement sensor, a plurality of electronic indicators to become sequentially activated at predetermined intervals when the differential pressure is higher than a set value; (c) correlating said intervals to the amount of time for which said differential pressure remains higher than said set value; and (d) determining the fouling status of the filter based on the number of said plurality of electronic indicators that are activated.
 14. The method of claim 13, wherein the electronic indicator is a light emitting diode (LED).
 15. The method of claim 13, wherein the electronic indicator is an auditory alert.
 16. The method of claim 13, wherein the electronic indicator is located remotely from the filter. 